This invention relates to a spindle motor for rotating a recording medium and a method of manufacturing a hub of the spindle motor.
Spindle motors have been put to wide practical use as motors for rotating recording mediums including magnetic disks or the like. In general, this kind of spindle motor has a housing mounted on a frame or the like of a drive unit, and a hub rotatable relative to the housing. In the case of a fixed shaft type, the shaft is fixed to the housing and the hub is rotatably attached to the fixed shaft with bearing members interposed therebetween. In the case of a rotating shaft type, the shaft is rotatably attached to the housing with bearing members interposed therebetween, and the hub is fixed to the rotating shaft. The recording medium, e.g., a magnetic disk is attached to the hub in a desired way.
However, in the conventional motors of this kind, the hub is manufactured by die casting or machining, and the following problems are therefore encountered.
In the case of forming the hub by die casting, cavities are formed easily and it is difficult to make the casting surface uniform because of occurrence of contamination or the like on the surface depending upon die casting conditions. Also, primary working is required to enable the cast piece to be used as a hub. (It is necessary to machine, after die casting, the cast piece at a position where a high degree of dimensional accuracy is required.) In addition, it is very difficult for the corner of the hub at which the cylindrical portion and the flange portion are connected to be made substantially perpendicular; a curved portion is left between these portions, which makes it difficult to attach the recording medium to the hub securely and substantially horizontally. Conventionally, such a curved portion is removed by machining but machining this portion entails the problem of generation of chips or the like.
On the other hand, in the case of forming the hub by machining, the amount of machining is considerably large, the manufacture cost is increased and it is difficult to improve the productivity.